Oxydosimeters are used by physicians and therapists to treat patients having chronic obstructive pulmonary diseases (COPD), such as emphysema. Typically, COPD patients exhibit symptoms ranging from a hacking cough, to a continual shortness of breath. These symptoms are known to therapists and physicians to possibly reflect hypoxia, a term which refers to a deficiency of oxygen in the blood, oftentimes due to impaired respiratory conditions. In general, hypoxia is defined as an average, or mean, blood oxygen saturation level less than 90%.
Oxydosimeters are also used to treat infants, or neonates, born with underdeveloped lungs. It is well known that neonates must be adequately oxygenated in order to avoid organ damage or, in the worst case, death. Frequently, clinical manifestations of neonatal hypoxia are subtle, although its effects may be rather severe later in life. For example, children who were hypoxic as neonates may suffer mental retardation from the lack of oxygen supplied to their body by their undeveloped lungs. On the other hand, care should be exercised to avoid delivering excessive oxygen, which may lead to retinal damage in young children.
A microprocessor-based device for treating neonates is disclosed in the article titled "Closed-loop Control of SaO.sub.2 in the Neonate," authored by Paul E. Morozoff and Ron W. Evans and published in the March/April 1992 issue of Biomedical Instrumentation and Technology. This device is used to maintain a preset oxygen saturation level in neonates so that the maximum amount of oxygen is delivered to the body. The system comprises a pulse oximeter utilized to gather patient data, a microprocessor to analyze the data and control the machine, and a motorized air-oxygen blender to provide the correct oxygen saturation level to the neonate. This device controls a mechanical valve separate from the mixer valves with servo-motors and potentiometers. With this device, however, a one-to-one mechanical-electrical correspondence is impossible. As a result, operators must frequently make manual adjustments to the device to maintain the desired blood oxygen saturation level of the patient.
It is, however, desirable to provide an improved method and apparatus for automatically maintaining the blood oxygen saturation level within desired ranges in neonates and to maximize the blood oxygen saturation level in adult COPD patients.